Nucleic acids are biopolymers that play a significant role in living organisms. The main role of nucleic acids is to store genetic information, however, there are also nucleic acids with functions, such as ribozymes and aptamers. As well as proteins, the function of nucleic acids is determined by higher-order structure. Therefore, it is essential to know the higher-order structure of nucleic acids for understanding the mechanisms of biological activities. Higher order structure is determined not only by nucleotide sequence but also by the external environment of the nucleic acid, i.e. the conditions of the solution in which the nucleic acid is solved. In this study, we focused on the effect of the external environment on the higher-order structure of nucleic acids and aimed to devise a new measurement method that can detect it. From our data, it was successfully detected by ITC that the G4 structure changes depending on environmental changes. If this method can be applied to various solution conditions, it should be possible to observe changes in the higher-order structure in response to more diverse environmental changes.